Why do relationships end?

[archerships]

From Monash University psych department:

Femlee (1995) studied the causes of breakups in university students,
and found that in 30% of cases the qualities which attracted people to
the relationship in the first place are also those that they ended up
most disliking about the person. These were qualities such as being
unusual, exciting and unpredictable, which represented a "fatal
attraction". An approach termed relational dialectics proposes that
close relationships are characterised by a tension between opposing
forces, such as autonomy and connectedness. So, we desire excitement
and newness in a relationship, but also being safe, secure and
understood. If a relationship begins with a heavy emphasis on one end
of a dimension, such as excitement and novelty, it will need over time
to be balanced by more predictability for the relationship to survive.

This raises the question, can a relationship appear to outsiders
doomed from the outset, while the lovers are blind to this
possibility? This question was studied by Macdonald and Ross
(1999). It would come as no surprise to learn that lovers were more
optimistic about the prospects of their relationship than observers
such as roommates and parents. Both groups of observers in fact were
more accurate than those in the relationship when asked to
specifically predict whether the relationship would last six months or
a year. However relationship members' assessments of relationship
quality were much better predictors of relationship stability, and
were also better predictors than observers' assessments of
relationship quality. So, love is not totally blind, in that the
lovers were better able to judge their relationships than outsiders,
but their direct predictions showed an optimistic bias reflecting
their aspirations for the relationship.